Quantum-well heterostructure laser diodes with flat widely tunable gain spectra

Abstract

For a novel type of asymmetric multiple-quantum-well heterostructure lasers it is shown that a flat modal gain spectrum is obtained in a wide spectral range. It occurs since the quantum wells varied in widths and chemical compositions give a definite contribution to the total gain in different intervals of the spectrum. A certain design of the laser structures (chemical composition, thickness, doping, and arrangement of active and barrier layers) provides the conditions of non-uniform excitation of the quantum wells that results in the broad-band flat gain spectrum. Output power characteristics of the tunable laser diodes with a grating external cavity are examined in detail. For the spectral interval near the wavelength of 820 nm, the GaAs-AlGaAs system is preferred. In this case, the width of the gain band reaches up 50 nm and the tuning curve is practically flat at the output power about 10 mW in a single-mode regime without mode hops. Use of the other ternary or quaternary semiconductor compounds transfers the tuning range to a necessary spectral region. The described quantum-well heterostructures are suitable to make effective tunable laser diodes for a wide variety of applications, such as WDM optical networks, coherent spectroscopy, chemical analysis, metrology, and environment monitoring.